Abrading apparatus



Jan. 15, 1952 w L, KEEFER 582,762

ABRADING APPARATUS Filed May 15, 1936 I5 Sheets-Sheet 1 I i J I I I I Vi x a 5 [Wk/fer j, fig? Jan. 15, 1952 w. KEEFER ABRADING APPARATUS 3Sheet at 2 Filed May 15, 1936 Jan. 15, 1952 Filed May 13, 1956 W. L.KEEFER ABRADING APPARATUS 3 Sheeis-Sheet 3 Patented Jan. 15, 19522,582,702 ABRADING AIIPARATUS' Walter L. Keefer, Hagerstown, Md.,assigncr to Pangborn Corporation, Hagerstown, Md., a

I corporation of Maryland Application May 13, 1936, Serial No. 79,559

This invention relates to abrading apparatus and more particularly tomechanical apparatus for propelling abrasives at abrading velocities.

Abrasive throwing wheels having bladed rotors have been known in the artfor many years, and.

although they are now going into rather wide use they are open to theobjection that valuable time is lost changing blades. The blades ofabrasive propelling rotors must be made removable, so that they may bereplaced when they have worn out, and yet must be held so securely thatthey will resist the tremendous centrifugal force exerted when the wheelis operating.

Also, in centrifugal abrading machines wherein the abrasive is fed tothe blades through an opening in a central feeding device and thedischarge is directionally controlled, it has been found that whenlarge. volumes of abrasive are fed to the machine the discharge streamwidens out to such a degree as to render the same undesirable forcertain installations, for instance when the machine discharges into awork tumbling barrel or drum.

The centrifugal abrading machines in use today are open to the furtherdisadvantage that the blades wear out rapidly, which entails highmaintenance costs. The blades would have a reasonable life if the wearoccurred uniformly throughout the width of their propelling surfaces,but it has been found that through casting or other inaccuracies,substantially all of the abrasive admitted to each blade will take acourse in a localized stream thereover when the blades are first placedin use, and as time goes on the blades will be deeply worn in thisparticular region with the result that all of the abrasive traversingthe blade will take this course, producing rapid break-down of theblade.

It is a primary object of this invention to provide an abrading machineblade assembly that securely holds the blades in place and yetpermitsthem to be removed and replaced in a minimum of time. 7 a

It is a further important object of the invention to provide a novelblade assembly for abrading machines that will hold all of the bladessecurely in place while the machine is operating, will permit easy andrapid removal and replacement of the blades when they wear out and whichwill also permit the blades to be removed and replaced in the machine ina different relationship to present different surfaces to the abrasivewhen certain of their surfaces have become worn.

A further object is to provide, in an abrading machine having a bladedrotor for propelling the blades of the invention.

7 Claims. (0]. 51-9) M abrasive, a novel blade mounting assembly whichwill securely hold the blades in place and will not work loose duringoperation of the machine, and which will permit the blades to be quicklyand 1.: easily removed from the rotor.

It is another object to provide a feeding mechanism for an abradingmachine which will deliver abrasive to the inner ends of the propellingblades in such manner as to enable the machine to deliver a concentratedstream of abrasive, even when abrasive is fed thereto in large volumes.

A further object is to provide an abrading machine with means forthrowing the abrasive splash back into the blades in such a. region asto cause the abrasive to discharge from the blades as though the splashhad not occurred.

A still further object is to provide abrading machines with bladeshaving means for causing the abrasive to take definite paths thereover,for

rendering uniform the wear that occurs thereon.

My invention also aims to provide an abrading machine with propellingblades which are so formed as to impart wear and friction reducingaction to the abrasive as it passes thereover.

It is also an object to devise blades for use in an abrasive throwingrotor which will produce a minimum blocking action and consequently aminimum splashing action when abrasive-is fed over their inner ends.

Another object is to provide an abrading machine with an adjustablefeeding device and to provide the adjusting device with means for makingit possible to disassemble the parts without disturbing the adjustmentof the device.

A further object-is to refine and improve certain detailed features ofcentrifugal abrading machines. I v

Further objects of the invention will become apparent as thespecification proceeds in connection with the annexed drawings, and fromthe appended claims.

In the drawings:

Figure 1 is a side elevational view of an abrasive propelling rotorequipped with the blade assembly of this invention, with parts thereofbroken away in order to more clearly illustrate the structure involved.I

Figure 2 is a' view looking at the wheel of Figure 1 from the right-handend of that figure, with parts broken away for clarity of illustration.Figure 3 is an enlarged fragmental sectional view illustrating themanner in which the blades cooperate with their locking screws.

Figure 4 is an isometric view of one of the Figure 5 is a transversesectional view taken on the line 5--5 of Figure 1, looking in thedirection of the arrows.

Figure-=9 is alongitud-inal sectional viewofa v further form of blade ofthe invention.

Figure 10 is a longitudinal sectional view of a further modified form ofblade of the invention- Figure 11 is an end view of the blade shown inFigure 10. V

Figure 12 is a-longitudinal seetional'viewofa still further modifiedform of abrasive propelling blade.

Figure 13 is a rear view of a modified form of y centrifugal abradingmachine also forming partof myjinyention and which shows a modified formof ad iugting mgchanism and indicates an inspeca tion. and vService'doorfor the wheel housing;

' Figure 14 is ailongitudinal sectional view'of- -th machine shown inFigure 13 and is taken .suble stantiall von line |4 l4 oi -that figure.

lIV-ithcontinued reference to' the drawings,

whereinjlike reference characters -have been em-r ployed to designatelike" partsthroughout the several yiews thereof; the rotor-isdesignatedat RI nti-111.115 rig y Btermirrate"shorter-the cen e rt0define a; central abrasive admitting: spacein whichan abrasive feedingdeyice-F-issupportedforrfeeding a stream of abrasive'over the-inner end10f blad s 'B- The f it effects, directional discharge of the abrasivethrown'from. the wheel, but; it "is to be understood that insofaras theblades andblade mountingare concerned; the invention is not limited to-aparticular feeding :device but may be applied toany type. of abradingmachine; ,7 For instance,

feet ling device 'F"may assume the form-of-a pipe- Secured to the faceof rotor R,-by -a plurality; of

countersunk screws I l are four symmetrically arranged plates l2:- Theradial edges" of plates P2 are providedwith bevelled faces l3; andtheadjacent edges of each pair of plates -defi-ne a dove-tail groove- M;as seen Figure-l Blades B are provided withcorrespondinglydove-tailshaped bases to fit in" grooves 14; andhave inclined faces l5cooperatingwith walls=-l3 of plate's lt The" inclined-faces 15 of-bladsBmerge into abrasive propellingsurfaces l 6--pro-- vided on-each-side ofthe blade.- 'As -seerrin' 1=ig-' ure- 1,- inclined faces l5 merge withplates 1 2 in'a region spaced from their propelling-'surfacesflli,with-*the result that= the abrasive=moving outwardly oversurfaces l6-issmaintained=out ofabradingacontactl with-plates [2; which are,permanent parts of'themachine; The-free edges of blades B are eachprovided with a flange or ridge I! to confine-theoutwardlymovingabrasivetoLsurfaceS: l6; a c

The blades are accordinglymountedlfor guided secured to a shaft HT;Shaft l 0. 15. mounted for rotation in'an-y desired bearing a sembly(not"'shown) and 1'0t0r-'R.' carr1es- -a plurality offabrasivepropellingblades -B.- Blades eed'device will'be presently described-andmovement toward and away from the axis of the rotor, and althoughgrooves M, which constitute the guideways, are shown as being disposedsubstantially radially, it is to be understood that they may be inclinedforwardly or rearwardly with respect to the direction of rotation ifdesired without departing from the uspiritjof the-invenion:

The means employed for, restraining blades B against outward movementpreferably takes the form of a screw IB, threaded into rotor Radjacent-'thegouter end of each guideway I4. Each screw isprovidedwith ahex head I9 which projects-into a-recess 2| in the base of each bladeBIQ JQ"gQqpdraitflshwith a wall 22 thereof to positively arrest outwardmovement of the blades. Thegfiatrsides ofhead I9 provide a large bearingsurface for wall 22 and also prevent screws l8fro'm working loose inoperation.

Referring to Figures 2 and 3, wall 22 and its opposite-wallare spaced-apart= a distance which is greater than-the-greatest diameter'of hexheads l9,-wi-th -the result that 'blades B can be slipped into placeingrooves Mend screws lfi turned up until they assume-the positionshownin Figure 3; Blades B may then be-pulled outwardly until takingthe-formof-a split resilient ring, encircling feed device F and engagingthe inner ends of the blades; may --be used to positively hold them inengagement with' screws l 8.

Although screws I8 may beprovided with any suitableformation topermitthem tobe turned home witha wrench they are preferably internallyformed with a hex socket-23 morder that v the screws maybe-sodimensioned as-to lie flush 18 into-a final position where a fiat sideofhex head 'lll will-be disposed in parallelism with wall22''of-'reeess-- 2| b'ecause the forces setup by retation of-the wheelwill 'cause the blades" to Work screws-I8 into the relationship shown inFigures 2 and 35 Screws I8 arepreferably designed, however, so that thefaces of-socket 23 and hex head) are disposed in registry, as seen'inFigure 3; with'the result that therelationshipof the surfaces of hexhead|9-to wall 22 of blade B may be determ-ined by merely glancingat socket23. Also, if a-wrench-=of; thetype-shown in dotted lines in Figure3 is;used, the relationship of the parts will i be f directly indicated by-the position of the=w re3 ch'-handle:

If-fhowever; theheads of screws- !8 are sodimensioned as to seat in thebottoms of recesses 2 l -wh'emthey are turnedhomeit is unnecessarytotake" any p artigzular precaution in installing the bladesbecausescrews 18 are thus automatically-stopped in approximately properposition andwil-l-assumeproperposition when the wheel isstarted;

seeninthedrawin s, whenthe screws are turned-home'a' clearance existsbetween their shoulders and the parts of blades B defining recesses-Zl;Although-a particularvformof locking assembly has been illustrated, itis to -be-understood that other forms of locking devices, whichthemselves are locked by the blades, may be used without departing fromthe spirit of this invention. For instance, instead of using screws l8,simple pins, having formations at their ends for interlocking engagementwith the blades whenthe latter are slid outwardly, may be used ifdesired. Moreover, hex head l9 may be made with more or less than sixsides if desired. Forinstance, square headed screws may be used ifdesired.

Referring now to Figure 4, each blade B is provided with two recesses 2|in its base and it is therefore symmetrical in form. The base of theblade also may or may not be cored out, as at 24. With the wheelrotating in the direction indicated in Figure 2, the abrasive is pickedup by and discharged from the counter-clockwise surfaces IB of blades B.By reason of the symmetrical design of blades B it is possible to removethe blades when they have become partially worn and reverse themend-for-end and thereby bring a new propelling surface into cooperationwith the abrasive. The worn surface is accordingly placed on theclockwise side of each blade. When the new surface has become worn theblades are of course discarded.

If an uncored blade is employed, it is to be understood that a singlerecess 2|, located mid-way between the ends of the blade, maybe used.Also, two screws 18 may be employed to hold each blade of the presentinvention in place, but it has been found that one screw is adequate,and the term a screw or a securing device as employed in the appendedclaims is intended to embrace the use of one or more screws It or theirequivalents.

As seen in Figures 1, and 6, feeding device F comprises a cylindricalmember 26 having an abrasive discharge opening 21 and a plurality ofexternal teeth having faces- 29 and 3|. Cylindrical member 26 issupported for adjustable rocking movement about the axis of the rotorupon a support S. Cylindrical member 26 is provided with a pair of studs33', which project through a pair. of arcuately-shaped openings 34provided in support S. A pair of nuts 35 are threaded on studs 33 andare operable to clamp feed device F to support S in any desired adjustedposition, for varying the direction of discharge from the wheel.

Support S is provided with a spout portion 31 through which the abrasivemay be admitted to the wheel and the abrasive fed through the spout isintroduced into the center of 'a hollow impeller 38 having a pluralityof blades 39. The forward face of each impeller blade 39 is concave intransverse section, and by reference to Figure 5, it is seen that eachimpeller blade inclines outwardly and rearwardly with respect to thedirection of rotation of the rotor.

The impeller is provided with a base portion 4| which is realeasablyclamped to the end of the rotor by means of a cap screw 42 or the like.The impeller is preferably, assembled in the machine so that eachimpeller blade is advanced a predetermined degree with respect to itspropeller blade B. The right-hand side wall of member 25 (Figure 6) isprovided withnotches (not shown) for allowing the impeller to be removedthere from.

It has been found that when a particle of abrasive leaves the tip of anabrasive propelling blade its direction is determined by the respectivemagnitudes of its radial outward velocity component and its tangentialvelocity component.

I have'found that .by inclining the blades of the impeller rearwardly,so as to diminish the tangential component and simultaneously'increasethe radial component, it is possible to make the abrasive dischargethrough opening 21 in container 26 to take the general path indicated bythe arrows45 in Figure 5. The abrasive discharged through opening 21 inthis manner assumes a more concentrated stream. The abrasive is thenpicked up by the inner ends of blades B passing;closely'adjacent opening21 and is smoothly and continuously accelerated until it reaches; theblade tips, where it is discharged downwardly in the approximatedirection indicated by the arrows '41. If it is desired to make themachine discharge in a direction other than that shown, nuts 35 may beloosened and cage 26 rocked in the proper direction to effect the de-'cation of opening 21; the speed of the wheel;

and the length of the blades, it is apparent that confining orconcentrating the angular range .over which admission or pick-up occurswill simultaneously limit or reduce the angular region over whichdischarge from the blade tips occurs. It is impractical to achieve thisresult by reducing the circumferential dimension of opening 21' becauseto do so would seriously reduce the capacity of the machine.

It has been found that inabrading machines of this character, especiallywhen large quantities of abrasive are fed thereto (from 15 to 25thousand pounds per hour), a considerable portion of the abrasive isstruck by the inner surfaces 48 of the blades, with the result that itrebounds back against the exterior wall of container 26. This reboundingabrasive, when containers having smooth exterior walls are used, is

reboundedoff the container and back into the path of the inner'ends ofblades B at points angularly remote from opening 21, with the resultthat the discharge point of such rebounding abrasive occurs aconsiderable distance from the discharge point of the main body of theblades B along with the main bodyof the abrasive discharge. 3

Although I have for sake of providing a com pact assembly, provided therebound teeth directly on the outside of conduit 26, it is to beunderstood that if desired, particularly if a plain feed pipe with noimpeller is used, the rebound teeth may be formed in a separate memberor members without departing from the spirit of my invention.

It is apparent that by inclining the imp'eua blades rearwardly so as toobtain a more nearly radial discharge of the abrasive through opening27, and by providing the exterior of casing 26 with teeth, theconcentration of the discharge of abrasive from the machine isgreatlyimproved. In some installations it may not be necessary to havean extremely narrowband of abrasive and in such case it will only benecessary to employ.

one of these features,-;and the appended claims.

7.? are; therefore; intendedv to; .eoverthe; two leatures eithers'singlyor in: combinatiom Inihe; presentxinstance, the impeller-wanes-are;

equal ;in;-,numb.er:-to;1 and; arezadvancediwithr re-. spect totheiripropeller; blades :B, with the me:

suit *that a a concentration; ofithe stream emittedj through opening1-2-1 occurs-,eachgtin'ie a; bladeeB;

om sinto abrasive :pickjip position; with the ;re=- suit t a th .;disharee ncentrating:action;is

urther i nhan e a In: Fi re; .8 an ifl-l hav illus rated modifiedforms-of blades that maybe used with-the machine thatahas j ust-,been';-described.. In :these figures itheblades are generally the samein for as those: shown: in Figures; 1 6' inclusive 'and thereforelikereference charaetershave been;em-- played-to designate correspondingparts through out the several vviews. I

Figure :2 the p op n s r e 'o b are of-corrugatedrform so as=,to providea pine rality. of valleys 55; It has been found that when-a blade ofthischaracter is, employed, theabrasive;,-jwhich is'introduced on the innerends of .the blades; is-oausedto'take a plurality of definite pathsoutwardly-moreover; with the re-' sultthat uniform-distribution of theabrasive is-mai-ntained until it'leaves the-tips of the blades,Avoidance of localized wear is accordingly achieved.

In tzliiigurefl, the-valleys 55 on one. surface. are aligned with thevalleys 55 on the other surface otthabl-ade with :theg'esult that thebladeis of non-uniform. section and. accordingly it; may be hardened at,somepoints more than others, .duriaotura nothe act r w ch. in-.

life of thiszbladeeover the ordinaryf erer t form of blade B which is:provided with; a. transversely corrugated abrasive propelling;surface-;5B.- In.v thisformaofithe invention, as.

the abrasive travels; outwardly" over thecorhea-tr contacts the bladesurface a limited-numbenof times, before it is discharged 'fromthe-bladetip,

videdwithtransverse corrugations that lie. flush with tor. projectslightly abovehthe outwardly extending corrugations so as'to confinetheiabrae siv ntod i nite outwardpaths and .yetto caus itflto strike theblade a limited'number'of times as it travels outwardly,

In figures '1 0'an.d' 11 I haveshown a, modified form of blade'B whereinthe blade isprovided with a; flat abrasive propellingsurface 6! Theblade of this and abevelled inner edge 62. formof the invention isirreversible and hence is provided=with only one side flange 63 which,as-

seen inF-igurell, provides aninclined abrasive guiding wall; Thablade is-also provided adja-- urfacelit2 only strikes the a tops of thecorrugations;- and 1in;v-iew of-= -the fact-that'-it only 8*; centstheajunctioni of: ab asiyei; propellin sure facejfilandxtheqbaseeofgthegb ade withza; long-l1 tudinal, groove-:6 41fo thezburpose of, providnsi' definite abrasive :confining. or guiding-wall so; as to preventabrasive from; abrading dovetail groove forming plates I 2.

With blades B 'installed in the wheel so as to rotate in the directionindicated in-Figure-lO,

it issapparent that as theabrasive is discharged from opening 21 in cage26; the abrasive ribbon will be sharply cut-:off; That is, there will:be

an abrupt break intheabrasive-ribbonas-allof the, abrasive preceding thebreak-will travel out-t wardly over propelling surfacefi-l and thesucceeding'part of the ribbon-will not contact theblade;

atall byreason of the-fact that wall 62 -iscut away sufliciently sothat'it moves away or re.-

cedestoo. rapidly for .the outwardly moving abra sive to strike it.

In- Figure 12 I have illustrated a-rblade similar to that shown in,Figures 10 and 11, but in this form of the invention the blade isprovided with a slightly-. bevelled inner end 65 and. a similarlzybevelledouter end-61.: In view-of the fact that; this formof blade isymmetrical itmay be;-1'8-.-

' versed in the same manner as. the blades-shown riace-bladeASJthincreasein area-.obr

in Figures 1, 2 and. 3. Although the bevel of the inner and outerends-ofthe blades shown in Figure 10 are notfveryi great, it has beenfound that with-(the usual. speed of: the abrasiveissuing from slot,2;lin. the, impeller cage. the abrasive travelsonly. approximately ofaninch while the blade is, traveling through. the;-

angle defined by thesinner Lends hithe -blades, and

therefore it 1 is 10 13., necessary to bevel thegbl'adeo parts to thisextent in order to prevent theabra sive from striking theabevelledface.-

In Figures -13 and 14;]; have-illustrated a modi-- fled formofymachinew-hereinthe impeller'cage is supported foradjustment in adifferent manner. In this form of the invention I have-shown a housingas being associated with the machine because certain parts of .themechanism are attached thereto.

Therotor is here-enclosed in a housing H having an inner liner -'H. AsseeninFigures 13-and 14, support Si is of; somewhat different-form thanthat shown in; Figured and iti'is provided a yoke member 79, whichis.in;;turn slotted and held -in place on the-machine by a pair ofheaded stud members 81.

By looseningscrew:18"yoke: member 19 may be slipped out from undertheheads of studs 81 and the closure- Hrremoved: A screw driver may then beemployed "to remove screws II so as to allow plate I2 to be removedfromthe rotor for servicing and" the like. Also, opening 76 provides aconvenient opening through which the condition of the blades may beobserved.

Secured to the rear face support S is an arcuately-shaped'stop plate 82having an arcuate slot 83ftherein'. Plate 82 is detachably clamped tosupport S by means of "a stud 84, which is fastened lnsupportS a nut-85and a collar 86;

r 9 The ends of stop plates 82 cooperate with the cylindrical portionsof nuts 35 in order to maintain cage 33 in proper angular relationshipin the machine.

For instance, it has been found that the machine may be adjusted for acertain type of abrasive and maintained in this adjustment so long asthe abrasive and the conditions under which the machine is used remainunchanged. When cage 26 is placed in this adjusted position, nut 85 istightened and maintains stop plate 82 in a position determined by nuts35. Therefore, when nuts 35 are removed and cage 26 replaced by a newcage, the cage must be installed in the machine in the correct angularrelationship as nut 35, when they are threaded on the studs of the newcage engage stop plate 82 and bring the cage into correct position. Inorder to indicate the angular position in which the cage is rotated, Ipreferably provide flange 72 with indicia 8'! which cooperate with arighthand nut 35 (Figure 13) to indicate the position at a glance.

Although it is preferably to employ the blade assembly with a rotorhaving but a single disc to which plates 12 are secured, the inventionis clearly applicable to rotors having two discs as the guideway and/orthe blade locking assembly may be duplicated on each disc.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is therefore to be considered in all respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States LettersPatent is:

1. In an abrading apparatus, an abrasive propelling rotor mounted forrotation and providing a central abrasive admitting space, a feed devicefor introducing abrasive into said space, a stationarily mounted supporthaving at least one arcuately shaped aperture, said feeding devicehaving at least one securing device projecting through said arcuateaperture and operable to clamp said feeding device in a plurality ofdifierent positions upon said support, and a stop member releasablyclamped to said support and having a portion cooperating with saidsecuring device for insuring proper assembly of said feeding device uponsaid support, thereby permitting said feeding device to be removed andreplaced without disturbing the adjustment thereof.

2. The abrading apparatus described in claim 1, wherein said securingdevice comprises a stud member fastened to said feeding device and a nutthreaded thereon and engaging said support and said stop member.

3. The abrading apparatus described in claim 1, wherein said stop membercomprises a member engageable with said securing device and having meanssecuring it to said support for movement into a plurality of adjustedpositions corresponding to the adjusted positions of said feedingdevice.

4. In an abrading apparatus, an abrasive propelling rotor mounted forrotation and providing a central abrasive admitting space, a feed devicefor introducing abrasive into said space. means mounting said feeddevice for rocking movement into a plurality of adjusted angularpositions about the axis of said rotor on a stationary support, meansfor securing said feed device in one of a plurality of adjusted angularpositions with respect to said support, and means for compellingassembly of said parts in a predetermined relationship, said last-namedmeans comprising an element having means for releasably clamping it tosaid support in a plurality of angular adjusted positions with respectto said support, said element being movable through a range of movementsubstantially equal to the range of movement of said feed device withrespect to said support.

5. In an abrading apparatus, a rotor having a plurality of outwardlyextending abrasive propelling blades mounted thereon, said bladesterminating short of the axis of said rotor to define an abrasiveadmitting space, said blades being operable to pick up' and propelabrasive admitted at a predetermined feeding zone in said abrasiveadmitting space, and stationarily supported means disposed in saidabrasive admitting space for rebounding back toward said feeding zoneany abrasive that may be improperly picked up by the inner ends of saidblades, said means comprising a member having a plurality of angularlydisposed rebound surfaces provided thereon and located adjacent the pathof rotation of the inner ends of said blades substantially equi-distantfrom the axis of rotation of said rotor, said surfaces each beinginclined at an obtuse angle with respect to a radial line intersectingsaid surface, said obtuse angles facing rearwardly with respect to thedirection of rotation of said rotor.

6. The abrading apparatus defined in claim 5, wherein a generallycylindrical abrasive feeding device is disposed in said abrasive feedingspace and said rebound surfaces are provided on said feeding device.

7. The abrading apparatus defined in claim 5 wherein a generallycylindrical abrasive feeding device is disposed in said abrasive feedingspace and said rebound surfaces are provided on said feeding device,said abrasive feeding device containing a rotatable impeller havingblades which incline outwardly and rearwardly with respect to thedirection of rotation of said rotor.

WALTER L. KEEFER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 391,971 House at al Oct. 30, 1888469,642 Nehr Feb. 23, 1892 1,052,291 Smoot Feb. 4, 1913 1,535,417 HuffApr. 28, 1925 1,789,874 Lilly Jan. 20, 1931 1,918,653 Martin July 18,1933 1,953,566 Peik Apr. 3, 1934 2,119,813 Keefer June 7, 1938 FOREIGNPATENTS Number Country Date 442,539 Great Britain Feb. 10, 1936 512,269Germany Nov. 8, 1930 519,837 Germany Mar. 5, 1931 784, 30 France s M y 13?

